1. Field of the Invention
This invention concerns lubricating oil compositions which are especially adapted for use in mechanical systems where gears are subjected to great stress and extremely high pressures such as those found in automotive rear axles or off highway transmissions and gear boxes. More particularly, the present invention relates to lubricants and functional fluids which are useful particularly in environments characterized by high pressure and rubbing surfaces.
2. Description of the Related Art
U.S. Pat. No. 3,082,187 (Fuchsmanf, et al, Mar. 19, 1963) broadly stated comprises a polyalkene having intimately dispersed therein (a) from about 0.005% to about 10% by weight of an organic phosphite ester having the general formula: ##STR2## wherein R.sub.1, R.sub.2 and R.sub.3 are each selected from the group consisting of hydrogen and hydrocarbon radicals containing from 1 to 21 carbon atoms, at least two of R.sub.1, R.sub.2 and R.sub.3 being a hydrocarbon radical; and (b) from about 0.005% to about 10% by weight of a sulfurized phenol having the general formula: ##STR3## wherein n is from 1 to 10, and R' and R" are each selected from the group consisting of hydrogen and alkyl radicals containing from 1 to 18 carbon atoms, at least one of R' and R" being alkyl.
U.S. Pat. No. 3,583,915 (Myers, Jun. 8, 1971) deals with the combination of a di(organo)hydrogen phosphonate, in which at least one organo group is an aliphatic group containing at least 14 carbon atoms, in admixture with an active sulfur compound evidences synergistic load carrying properties in organic base media.
The di(organo)phosphonates have the structure ##STR4## wherein R and R' are individually alkyl or alkenyl from 1 to 30 carbon atoms and at least one of which is an aliphatic group of at least 14 carbon atoms, and preferably over 16 carbon atoms. These groups may have the same number of carbon atoms or different, and one may be further substituted by the presence of alkoxy, hydroxy and halogen substituents. Dioctadecyl and dioleyl phosphonates are of particular interest. The phosphonates used may be produced by known methods of synthesis.
The second co-additive may be designated as an active sulfur compound. The compounds of this class include organic sulfides and sulfurized hydrocarbons having up to 65% sulfur. Encompassed in this class are those compounds wherein the sulfur is "loosely-bound," and the non-corrosive or "firmly-bound" sulfur compounds. More specifically, such compounds include sulfurized animal and vegetable oils and fats and mineral oils containing at least 1% and up to 20% sulfur; up to about 10% for "firmly-bound" and from about 10% to 20% or more for "loosely-bound"
U.S. Pat. No. 3,446,739 (Papayannopoulos, May 27, 1969) provides organic compositions which contain additives effective for imparting limited-slip properties thereto, but which do not detract from the extreme pressure properties of such compositions.
These organic compositions comprise an alkyl phosphite and an ester of a fatty acid and a fatty alcohol, wherein alkyl groups of the phosphite and alkyl groups of the fatty acid and the fatty alcohol each contain from about 12 to about 30 carbon atoms. In general, in its preferred applications, this patent contemplates organic compositions exhibiting effective extreme pressure properties under varying operating conditions, and which also contain a small amount of the above-described additive limited-slip improver mixture, usually from about 0.1% to about 40% by weight, and preferably from about 0.5% to about 10% by weight of the total weight of such composition. Insofar as the additive mixture itself is concerned, the alkyl phosphite is present in an amount from about 10% to about 90% by weight, and, correspondingly, the ester is present in an amount from about 90% to about 10% by weight of the total weight of said mixture.
U.S. Pat. No. 3,321,401 (Ford, et al, May 23, 1967) provides for lubricating compositions containing a combination of additives that has the effect of improving the load-carrying properties of the compositions.
According to the patent, there is provided a lubricating compositions comprising a lubricating base oil having dissolved therein small proportions each of (a) an organic phosphite of the formula: ##STR5## where the R.sup.1 s are alkyl, cycloalkyl, aryl or aralkyl groups and the total number of carbon atoms in the molecule is 1 to 20 and (b) another oil-soluble organic phosphorus compound of the general formula: ##STR6## where X is an oxygen or sulfur atom and Y is R.sup.1 O - - - or ##STR7## where R.sup.1 has the value previously given, R.sup.2 and R.sup.3 hydrogen or alkyl, cycloalkyl, aryl or aralkyl groups or together with the nitrogen atom form a ring which, apart from the nitrogen, is made up of hydrocarbon groups or hydrocarbon groups and a second hetero atom, e.g. oxygen, and the total number of carbon atoms in the molecule is 1 to 30.